Friday, March 11, 2005

The Extinction Cycle

Two physicists at UC Berkeley claim to have uncovered a suspciously regular cycle of mass extinctions stretching back the Cambrian explosion. Apparently, an extinction event occurs every 62 million years or so (which, as Arthur Chrenkoff notes, makes us about 5 million years overdue.) The scientists involved make some guesses as to the possible cause of these periodic extinctions: comet showers brought on by the sun's orbit through the galaxy, or a cycle of mass volcanism. Apparently there's even some evidence for catastophic volcanism around the time the dinosaurs bit the dust.

My guess, though, is that neither of those explanations will turn out to be right. My geuss - based on nothing more than a hunch - is that the cycle is an epiphenomenon inherent to living systems, the same way market crashes are inherent to stock markets. Ecologies are massively complex, dynamically metastable systems: a small perturbation might do nothing, but it might also throw the entire system into a new metastable state. The transitional period is the mass extinction.

Now, the perturbation might well be an external factor - a comet impact, for instance - or it might be internal, like the evolution of a new species. What happened billions of years ago when the first bacteria learned how to turn sunlight into energy, and as a result started polluting the atmosphere with oxygen? Oxygen is highly reactive, and severely toxic to the anaerobic bacteria that - up to then - had dominated the planet. Similarly, what happened to other species when eyes were first developed? From our perspective, these developments were necessary and probably inevitable; at the time, they were catastrophic.

Note that the two broad classes of explanation - external versus internal factors - are not mutually exclusive. I have a feeling, however, that the internal factors will turn out to account for much of the observed periodicity, though, like I said, that's just a hunch.

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